1. Field of the Invention
The present invention relates to an image forming apparatus applied to a printer or a copying machine which performs image formation e.g. by electrophotography.
2. Description of the Related Art
Conventionally, image forming apparatuses, such as a copying machine and a printer, use a technique of calibrating an output image. For example, there has been proposed a technique of improving image quality by forming a certain specific pattern on a recording sheet, subsequently reading image information, such as density, chromaticity, etc. of the formed pattern, by an image reader unit, and then configuring image forming conditions based on the image information (see Japanese Patent Laid-Open Publication No. S62-296669 and Japanese Patent Laid-Open Publication No. S63-185279).
However, in the above-mentioned prior art, a recording sheet for use in calibration is limited to a specific type so as to improve the stability of image quality. This leads to a problem that if an image is recorded on a different recording sheet from the recording sheet for calibration, image characteristics are not ensured.
As a solution to this problem, it can be envisaged to add a recording sheet type that can be used for calibration. More specifically, in adding a recording sheet type usable for calibration, calibration is performed on a recording sheet of a specific type first, and then in a state where a result of the calibration is set, a predetermined image is recorded on a recording sheet of the type to be added. Then, the predetermined image recorded on the recording sheet of the type to be added is read by a reading unit. Further, based on image information read from the predetermined image recorded on the recording sheet of the type to be added, settings for converting image information read from the predetermined image on a recording sheet of the type to be added are generated and stored. Then, in the case of performing calibration using a recording sheet of the added sheet type, image forming conditions are configured based on the predetermined image on the recording sheet and the settings.
However, if an image forming apparatus having a plurality of reading units is used, the above-described method suffers from the following problem:
Different reading units deliver respective outputs which are different in image characteristics even when the same object is read. Therefore, it is required to configure settings for converting read image information on a reading unit-by-reading unit basis. For this reason, even if one reading unit adds a recording sheet and store settings for converting read image information, by the above-described method, the settings cannot be applied to an another reading unit. In short, to enable reading units to cope with a recording sheet to be added, it is required to manually configure settings for converting image information, on a recording unit-by-recording unit basis, which takes much time and labor.